1. Field of the Invention
The invention pertains to a method and apparatus for permitting electronic machine vision of light reflecting objects wherein a true observation of the surface being viewed is obtained by masking potential reflections resulting along the observation axis due to observation windows and cameras, or other non-illuminating discontinuities in the illumination environment.
2. Description of the Related Art
Electronic machine vision apparatus is commonly employed in conjunction with automatic machining, assembly and inspection apparatus, particularly of the robotic type. Television cameras are commonly employed to observe the object being machined, assembled, or inspected, and the signal received and transmitted by the camera can be compared to a standard signal or database to determine if the observed article is properly machined, oriented, or assembled. Also, machine vision apparatus is widely used in inspection and flaw detection applications whereby inconsistencies and imperfection in both hard and soft goods can be rapidly ascertained and adjustments or rejections instantaneously effected.
Machine vision apparatus detects abnormalities by comparing the signal generated by the camera with a predetermined signal indicating proper dimensions, appearance, orientation, or the like. In order to achieve consistent and accurate results when using machine vision apparatus employing electronic cameras, it is very important that consistent and uniform lighting of the observed object occur, as the lighting will seriously affect the vision signal generated and produce irregular signals even though no fault may exist in the object being observed other than it is not uniformly illuminated.
Illumination problems in machine vision applications are particularly present when the object being observed has a shiny specular surface. For instance, in the inspection of soldered circuits such as used with printed circuit boards the highly reflective nature and uneven surface geometry of the solder makes it very difficult to obtain an accurate electronic signal, and the same is true when machine vision inspecting ball bearings, reflective packaging, and other objects having shiny surfaces, particularly irregular shiny surfaces.
When utilizing machine vision techniques and apparatus in shiny surface applications, it is common to employ complicated lighting systems for illuminating the object being observed, and it is a purpose of such lighting systems to eliminate shadows, highlights, underlights, reflections and other lighting characteristics caused by shiny convex surface objects. Examples of complex lighting systems for use with machine vision apparatus are shown in U.S. Pat. Nos. 4,677,473; 4,882,498; 5,051,825; 5,060,065 and 5,072,127. While devices shown in these patents are capable of generating improved lighting characteristics, such devices do not eliminate erroneous signals resulting from the reflection of windows, openings or orifices defined in the lighting apparatus necessary to permit observation of the article being viewed, and such apparatus does not eliminate erroneous signals generated due to the reflection of cameras, openings or voids from specular objects.